This invention relates to the separation of the formed elements or the heavy phase of a blood sample, i.e., white cells, red cells and platelets of blood, from the serum or plasma or the light phase of the blood.
Such separation is typically performed by centrifuging a blood sample so that the heavier phase is forced to one end of the blood sample and the lighter phase is forced to the other end of the blood sample.
After such separation by centrifugation, it is desirable to physically separate the formed elements of the blood from the serum or plasma in order to prevent the contamination of the serum or plasma. Such contamination can occur as the red blood cells begin to liberate potassium and other contaminants which might interfere with tests performed on the serum or plasma. It is also possible that any fibrum which remains in the sample may produce some contamination.
In order to achieve this isolation or fluid separation of the formed elements of the blood from the serum or plasma, self contained separator assemblies of the Vacutainer type have been suggested. Examples of such Vacutainer assemblies are shown in U.S. Pat. Nos. 3,891,553, 3,894,951 and 3,894,952.
Such blood separation apparatus typically comprises a collection container having elastomeric plugs sealing opposite ends of the container with a piston-like plug located within the container and forming a seal with the walls of the container. A partial vacuum is created on the interior of the container so as to assist in drawing the blood sample into the container through a cannula which penetrates one of the end plugs. The plug which is characterized by an average specific gravity greater than the light phase of the blood comprises a pressure-responsive valve which, under the force of centrifuging and the pressure of serum or plasma against the valve, will open the valve to allow the plasma or serum to pass therethrough. The plug typically also comprises a filter member associated with the valve to prevent fibrin or formed elements of the blood from clogging or passing through the valve. As centrifugation continues, the plug will stop at the interface between the light phase and the heavy phase as the filter becomes clogged with the elements of the heavy phase. Once centrifugation is completed, the light phase should be on one side of the plug and the heavy phase should be on the other side of the plug.
Reliance on the clogged filter to stop the plug at the interface of the light phase and the heavy phase can result in lysing of the blood cells due to the pressure placed on the cells by the clogged filter. Once lysing occurs, any contact between the lysed cells and the serum or plasma will produce contamination of the serum or plasma.
It has been found to be particularly desirable to utilize the separator assembly in and of itself as a transport apparatus for transporting the blood sample to the laboratory from the point at which the blood sample is taken. This requires the valve of the assembly to close tightly after centrifugation and remain closed so as to prevent any contamination between the two phases of the blood.
Heretofore, valves of self-contained separator assemblies have in general relied upon the elastomeric properties of the plug or valve to return the valve to the closed condition, i.e., there is no force or bias acting on the valve after centrifugation to hold the valve closed. Rather, the valve elements, when properly structured, merely contact one another when returning to a natural or unbiased state. Closure of these valves may be assisted by the tubular member of the container if the inside diameter of the tubular member is slightly smaller than the outside diameter of the plug but the tolerances on the inside diameter of the tubular member are difficult to control particularly where the tubes are extruded.
A further difficulty associated with such separator apparatus is a result of the necessity for the valve to open with the force generated during centrifugation and still close after centrifugation.
Similar characteristics may be found in the valve structures of my U.S. Pat. Nos. 3,661,265 and 3,799,342 where plunger type serum separators are adapted to serve as transport devices. U.S. Pat. No. 3,954,614 also discloses a valve in a serum separator which is characterized by little or no seating forces when the valve is in the closed position. The same is true with respect to U.S. Pat. No. 3,962,085 wherein the periphery of the disc acts as a valve which is closed when the disc is in the closed position. However, there are no substantial seating forces beyond the weight of the blood sample itself. Valves such as those shown in U.S. Pat. Nos. 1,777,408 and 2,191,636 are biased so as to provide a substantial seating force when in the closed position, but such valves are too complex for use in serum separators.